Cryogenic System for the Production of Very Thin Targets

Abstract

A windowless gas target cham her has been developed for the production of very thin, but uniform, targets to be used with accelerated charged particle beams. The target reaction chamber is appended to a cryostat which is capable of containing liquid helium as the primary refrigerant. The temperature of this chamber can be adjusted so that condensation of the gas in the vicinity of the beam path is minimized. The cryostat freezes out the gas which escapes the reaction chamber. To date, we have used this new cryogenic technique to observe the'D(d,n) reaction and the (p,n) reactions in uB, 4°A, and 37el. Very narrow resonances (widths :::;450 eV) were discovered in the 4°A(p,n)4°K reaction near the neutron threshold. The narrowest observed widths in the yield curve are 140±10 eV. These were observed with a target whose effective density was found to be 3.0±0.3X 10 16 atoms/em'.